With recent development of wireless communication technology, systems of various kinds that use different communication schemes coexist. For example, a system that uses a Code Division Multiple Access (CDMA) scheme called a second generation technique coexists with a system that uses an International Mobile Telecommunication (IMT)-2000 scheme, called a third generation technique, and a system that uses an Orthogonal Frequency Division Multiplexing (OFDM) scheme, called a fourth generation technique.
The coexisting systems that use different communication schemes provide a service to users using different frequency bands. However, since a frequency resource for wireless communication is limited, the frequency resource is insufficient for lots of systems to coexist.
Accordingly, a CR technique of using a frequency band or a channel that is not used temporarily among frequency bands already assigned and used is being studied. That is, even a system that is licensed for a specific frequency band does not always use all relevant frequency bands. Therefore, a CR-based wireless communication system searches for a channel that is not used temporarily by a system having a license, and then provides a service to users inside a service area through the searched channel. For example, of frequency bands assigned for transmission of TeleVison (TV) signals of 1 GHz or less, frequency bands not used temporarily can be used.
In the case where a wireless communication system applies a CR technique, base stations in charge of respective cells have to share communication information of other base stations in order to efficiently share a frequency resource. For this purpose, base stations in charge of respective cells in the CR-based wireless communication system transmit a Coexistence Beacon Protocol (referred to as “CBP” hereinafter) packet including communication information of the base stations themselves to adjacent base stations via a Self-Coexistence Window (SCW) slot, and the adjacent base stations receive the CBP packet, so that the communication information is shared. Here, the SCW slot is located at a predetermined position of every frame, and the CBP packet includes various information related to a self coexistence algorithm such as a location of a relevant base station, a sensing result, scheduling information, and a backup channel list.
As described above, in a CR-based wireless communication system, base stations share communication information regarding respective cells by transmitting and receiving a CBP packet via a SCW. However, since the SCW is a resource of a limited amount, in the case where a plurality of base stations intends to transmit CBP packets, a collision of the CBP packets occurs. When the base stations cannot normally receive a CBP packet from an adjacent base station due to collision of CBP packets, a system cannot operate swiftly. Therefore, in order to allow a CR-based wireless communication system to normally operate, an alternative for transmitting/receiving a CBP packet without collision or an error is required.